I'm wondering this as well.
Even Sony's getting into the game with the little PlayStation TVs that pair back to the PS4 for remote play, access downloadable PSOne/PSP/Vita game, and cloud services for PS3 games. Basically the three core functions we've been asking out of the AppleTV for a while now. The AppleTV will kinda do the former with AirPlay mirroring, but you still have have the controls trough the primary device.
The Chromecast is out and does the only real function of the AppleTV for less (device mirroring) provided it can run some flavor of Chrome.
The Microsoft Miracast exits, for what that's worth.
SteamOS with desktop sharing and various flavors of SteamBoxes are rolling along kinda sub rosa.
Apple's kinda leaving it a bit too long, and really starting to bloat out the AppleTV's screen with "partner channels". Yes, bloatware. The only thing the AppleTV has going for it, that other devices aren't allowed to do is use the AirPlay protocol. Everything else other companies are doing, and arguably doing far better.
I've been tasked with getting my parents updated from a nearly decade and half-old CRT to a new "digital" setup and am shopping for middle-man boxes between their older entertainment cabinet and the new TV. They are a very Mac heavy household, but I can't justify the AppleTV as it exists. The lack of HDMI pass-through kills it almost immediately, without even looking at other missing functions.